Genetic engineering is one of the most important technologies now available to scientists. The technology was crucial to the sequencing of the human genome, and has greatly increased the potential for developing new medicines.

Genetic engineering is the process of removing a gene from one organism and putting it into another. Often, the removed genes are put into bacteria or yeast cells so that scientists can study the gene or the protein it produces more easily. Sometimes, genes are put into a plant or an animal.

One of the first genetic engineering advances involved the hormone insulin. Diabetes, a medical condition that affects millions of people, prevents the body from producing enough insulin necessary for cells to properly absorb sugar. Diabetics used to be treated with supplementary insulin isolated from pigs or cows. Although this insulin is very similar to human insulin, it is not identical. Bovine insulin is antigenic in humans. Antibodies produced against it would gradually destroy its efficacy.

Scientists got around the problem by putting the gene for human insulin into bacteria. The bacteria's cellular machinery, which is identical to the cellular machinery of all living things, "reads" the gene, and turns it into a protein-human insulin-through a process called translation.